The low parts within the region are in the beds of the arms and lakes on the:
Chilia arm (-36m)
Sulina arm (-18m)
Saint Gheorghe arm (-26m)
Then the lakes:
The highest altitudes are on the Chilia bank (6,5m), Letea bank (13m), as well as in the area of the Caraorman dunes, in the region of the Razelm lagoon complex, where the rocky islands of Bisericuta (4m) and Popina (49m) are located.
The hydrographic network of the delta is of a particular interest from the geographic, economic and tourist point of view. The hydrographic network supplies the lakes with water, with mineral and organic substances brought by the water, and secures travel to areas where it is not possible to go on foot.
This network includes: the Danube arms, backwaters, and canals. As to the arms, they are four, of which only three have mouths at sea: Chilia, Sulina and Saint Gheorghe. The Tulcea arm is defined between the two “ceatals” (as the arms ramifications are called there) Chilia and Saint Gheorghe. The Tulcea arm and the Chilia arm initially were one of the two delta arms. Later on, the other two arms separated: Sulina and Saint Gheorghe. In order to avoid certain confusions, some researchers consider that only three arms should be taken into account: Chilia, Sulina and Saint Gheorghe.